WHY

There are often MANY different ways to solve a problem you may post....that is why there are often several answer methods with the same result....We do not know what you are being taught, how far along you are in your math studies or how old you are.....often the posted questions are incomplete or rather ambiguous, so everyone gets to post THEIR methods of getting a final answer and hopefully one will be compatible and congruent with your level of math knowledge.....

Just sayin'    ......